1. Field of the Invention
The present invention is related to the field of pressure responsive valves, particularly those as used in fuel injectors for internal combustion engines for draining of fuel and timing fluid when predetermined fluid pressures are exceeded, and as is used in other applications where fast, predictable response times and minimum space requirements are prime considerations.
2. Description of Related Art
The competing demands for increased fuel economy and improved pollution control has led internal combustion engine designers to give increased attention to improvements in fuel supply systems, particularly fuel injection systems. However, these efforts have lead to more complex designs and more demanding performance characteristics, and has required the number of components to be increased and the size to be decreased.
For example, U.S. Pat. Nos. 4,721,247 and 4,986,472 (which are owned by the assignee of this application) address the problem of achieving the high injection pressures (on the order of 30,000 psi and above) required to reduce the levels of hydrocarbons, nitrogen oxides and particulate mass over the entire range of engine operating speeds. Furthermore, to achieve adequately high pressure at low engine speed without excessive pressures being generated at high engine speeds, the fuel injectors of these patents use a coil spring-loaded, pressure responsive valve to drain timing fluid from a timing chamber, that forms an intermediate hydraulic link in an injection plunger assembly, whenever the pressure of the timing fluid exceeds a predetermined value.
While an improvement over then existing fuel injections systems, such fuel injectors do not represent an optimized design, at least in part due to the fact that coil spring type relief valves can be subject to slow response rates resulting in pressure oscillation and valve chatter affects the ability to obtain adequate pressure regulation. Furthermore, due to the relationship between spring rate and springs size inherent in helical coil springs, the use of coil springs for the pressure responsive component of a valve imposes size constraints on the extent to which the size of a fuel injector, or any other device using such a valve, can be reduced. Also, coil springs are subject to spring relaxation which can affect the reliability of the precision pressure control achieved thereby.
Pressure responsive valves have long been known for use in a variety of environments in which a band-like spring element serves as the pressure responsive component for opening or closing a fluid port. In many cases, as shown in U.S. Pat. Nos. 4,708,156 and 4,194,435, the band member is a resiliently stretchable ring that is made of rubber or a rubber-like material and is mounted in tension over an annular surface containing at least one port. When the fluid pressure becomes great enough, it stretches the band so as to uncover the port to permit the outflow of fluid. However, such elastomeric bands cannot be subjected to either high temperatures or high pressure levels, such as those experienced in high pressure fuel injectors.
Pressure responsive control valves using band-like spring elements of metal are also known (see, for example, U.S. Pat. Nos. 233,432; 4,095,617; and 5,014,918). In the case of the air compressor of U.S. Pat. No. 233,432, a band-like ring valve is beveled at each side and is received in a beveled seat which flanks an annular opening in a circumferential wall of a compression cylinder. To allow the ring valve to expand to allow air being compressed to exit the opening, the ring is cut or split; but, to close the annular opening at the split, a joint or cover is attached to the ring, or the ends of the ring are oppositely tapered and made to overlap each other, or a double-ring arrangement, in which the cuts of the rings are on opposite sides, is provided.
In contrast, in the airblast fuel injector for gas turbine fuel injectors Of U.S. Pat. No. 5,014,918, a spring valve in the form of a cantilever reed valve is formed of a partially cylindrical, arcuate band-like member that is machined from tubing stock. The spring valve lies against the inner surface of a cylindrical seat member. One end of the spring member is attached to the seat member by set screws at an area diametrally opposite the fuel outlet port formed in the seat member.
While the band-like valve spring members of the preceding two cases may be suitable for situations in which the pressure of the fluid being regulated is not that great and/or a high degree of precision is not required, such spring members would not be able to meet the demands for precision control that are necessary in high pressure fuel injectors for internal combustion engines that are being designed to have increased fuel economy and improved pollution control characteristics because such high performance injectors require fast response times and must meet minimum space requirements. Furthermore, in comparison to a continuous annular valve spring member, such split valve spring members are more difficult to make and install.